This disclosure relates generally to turbofan engines and, more particularly, to turbofan engines having a variable area fan nozzle. In particular, this disclosure relates to variable area fan nozzles that comprise a plurality of circumferentially arranged petals for varying the exit or throat area of the nozzle.
One approach to increasing the fan nozzle throat area as a means to reduce noise generated during high-thrust events such as during takeoff is through the use of movable rigid flaps or petals which form the fan nozzle exit external boundary. These rigid flaps or petals may be deflected outwardly to enlarge the throat area of the fan nozzle and thereby reduce the exhaust velocity or, conversely, they may be deflected inwardly to reduce the throat area of the fan nozzle and thereby increase the exhaust velocity.
An additional consideration in a variable area fan nozzle for reducing exhaust noise is that a movable fan nozzle must be compatible with thrust reversers commonly employed on modern turbofan engines. As is known in the art, thrust reversers on turbofan engines may reduce landing distance of an aircraft in normal (e.g., dry) runway conditions or increase safety in slowing the aircraft in slick (e.g., wet) runway conditions. Thrust reversers operate by reorienting the normally aftward flow of exhaust gasses into a forward direction in order to provide braking thrust to the aircraft. The reorienting of the engine exhaust gases is facilitated by spoiling, deflecting and/or turning the flow stream of the primary exhaust and/or the fan exhaust.
For turbofan engines, thrust reversers may include the use of cascade baskets, pivoting doors or by reversing the pitch of the fan blades. In a cascade-type thrust reverser, the turbofan engine may include an outer axially translatable thrust reverser sleeve which is configured to move axially aftward to uncover cascade baskets mounted in the nacelle cowl and comprising a multiplicity of flow-deflecting vanes. Simultaneous with the aftward movement of the translating sleeve, blocker doors in the fan duct are closed in order to redirect the fan flow outwardly through the flow-deflecting vanes and into a forward direction to provide thrust-reversing force. In some implementations, the cascade baskets are disposed between the thrust reverser sleeve and the portion of fan duct outer wall connected to the thrust reverser sleeve. Due to the widespread implementation of thrust reversal capability on many aircraft, a variable area fan nozzle must be compatible with thrust reverser systems commonly employed on modern turbofan engines
It is known to vary the area of the fan nozzle (thereby modulating the fan flow) by deflecting flaps or panels (hereinafter “petals”) which are hinged to the trailing lip area of an axially translatable thrust reverser sleeve. As used herein, the term “thrust reverser sleeve” includes at least the following configurations: (1) a one-piece axially translatable sleeve that extends around a major portion of the circumference of the fan duct, from one side of the engine pylon to the other; and (2) two axially translatable half-cowls mounted on rails fixed to upper and lower beams and extending from the upper beam to the lower beam. In accordance with the latter configuration, the upper beam is the main hinge beam that allows the half-cowls to open for engine access and removal. The lower beam (referred to hereinafter as “latch beam”) provides a means for locking the two half-cowls together. Thus the second configuration typically has two upper hinge beams and two latch beams.
A variety of solutions for actuation of a variable area fan nozzle exist, but there is room for improvements.